Manipulating oilseed rape canopies through the season using fungicides and attention to detail is well accepted as the key to boosting yields.

Gross margins are so tight now that crops cannot be left to compensate for poor establishment and will need more management input if the crop is to remain economically viable.

These are the comments of arable farm manager, David Fuller, of McGregor Farms, Coldstream, who last year, despite atrocious weather conditions, managed to produce a satisfactory margin from a crop of Incentive oilseed rape that spent more time of the winter period under water than above it.

“Oilseed rape must establish well to reach full potential and this is where the input investment should be made. Investing in a robust fungicide programme, where products are selected for disease control as much as crop manipulation will continue to play a key role in our management strategy based on our experiences last year,” he said.

McGregor Farms is a 3200 ha family business that grows combinable crops, potatoes and vining peas mostly on sandy clay loam soils within a 10-mile radius of Coldstream in the Scottish Borders. Feed wheat and oilseed rape five year average yields are 9.8t/ha and 4.7t/ha, respectively.

Oilseed rape has become an increasingly important break crop for the business with 560 ha now being grown.

“There’s no other suitable breakcrop really this far north that gives us the entry to first wheat,” said Mr Fuller. “We don’t have blackgrass up here yet, so delayed drilling isn’t such an issue for us, but limited drilling days are, so we have to get one crop off and the land prepared for the next one in a short time window.”

Establishment can be a big challenge, particularly as August is normally a wet month, with 100mm of rain not uncommon. Autumn establishment is, therefor,e key and the plan is to drill low seed rates – around 40 seeds/m2 – aiming for about 25 plants/m2 by the spring. This should ensure large strong stems full of pods.

“Most crops grow away well in the autumn, but occasionally will then struggle and it’s these crops that need growth manipulation and effective light leaf spot control,” explained Mr Fuller. “We grow varieties that offer good resistance to light leaf spot as this gives us an extra line of defence against the disease.”

Until now, he has applied his first light leaf spot spray based on prothioconazole or tebuconazole, depending in the need for growth regulation, by late October to early November.

Delaying this application any later risks not being able to treat the crops until the spring, as spray days are very limited in December and January, he argued.

On very forward crops, the preference would be tebuconazole's greater growth regulatory effects than prothioconazole. On crops where establishment would benefit from a boost to vigour, the product of choice is Refinzar (penthiopyrad + picoxystrobin) at the same timing.

The Refinzar not only has activity on light leaf spot, but also has the added benefit of increasing root mass. “It’s very difficult to predict yield on oilseed rape,” said Mr Fuller. “You can have a feel for it but then hope that mother-nature kicks in.

"We want to get a robust crop in the spring, but this often needs help to push through to the summer. The increased root development provided by Refinzar may help make this less of a lottery.”

Oilseed rape is drilled straight into stubbles with a Simba SL on 430mm row widths. Liquid starter fertiliser (phosphorous, nitrogen and boron) is placed next to the seed. It is a one pass system.

“Refinzar was used last year in a 5 ha field trial running alongside the River Tweed,” explained Mr Fuller. “It was the last field drilled using a variety called Incentive at a seed rate of 40ppm2 in good conditions on August 28. Spray timing was early November.”

What proceeded thereafter was a prolonged period of torrential rain on nothing short of biblical proportions. The trial plot had established well and by early December was at the eight-leaf stage, but, on December 5, after heavy rain the Tweed burst its banks leaving the crop six feet under water for three days.

Four further floods with the crop under water for four days on each occasion and he feared for the worst. Boxing Day saw the biggest flood.

“I was surprised that anything survived, to be honest,” added Mr Fuller. “The crop looked awful, with plants covered in mud and silt and only the green point of the plant left, but the Refinzar treated plot did have big roots.

"The crop had established well due to good drilling conditions and a mild winter. The root mass would have developed before the flooding, which must have helped get the crop through.”

By late April, after the waters had receded, he said crops evened out and it was hard to tell the difference between the forward and backward crops.

“Last year wasn’t a particularly bad season for disease on the whole, probably because the crop spent large periods under water and most of the plants had been defoliated from the flooding.

"The oilseed rape was quite late coming into flower too and with the variety Incentive only scoring a six for light leaf spot, it needed the Refinzar to give it some additional disease control," he said.

“The results speak for themselves and, where crops will benefit from a boost to establishment in the autumn, we will be using it again simply because the extra rooting in addition to light leaf spot control are reason enough to include it as part of the oilseed rape fungicide strategy,” he said.

“On more forward crops, if necessary, we will go with tebuconazole in the spring using half rate for light leaf spot and, if we want to manipulate growth, then we might use a higher rate.”